Our long term goal is to define the mechanism for the mitochondrial defects during heart failure and to devise mechanism-based therapies towards these defects as new approaches to the treatment of heart failure. There is now compelling evidence of electron transport chain abnormalities in both animal models and human heart failure, but the molecular bases for these defects and their role in the pathophysiology of heart failure remain unclear. Abnormalities in mitoch0ndrial morphology, and in complexes I, III, IV and V of the electron transport chain have all been reported in either specific animal models of heart failure or human hearts from patients with heart failure. Thus, while impaired ATP production via oxidative phosphorylation may be a common theme in the failing heart, the specific abnormalities may be dependent on the heart failure model studied, or the etiology of the heart failure in patients. This proposal is designed to test the hypothesis that the microembolism-induced heart failure model is associated with damage to cardiolipin, which limits complex IV activity, and thus myocardial ATP availability, while the pacing-induced heart failure model induces a defect in complex III, which again limits ATP availability. A relevant issue is whether the mitochondrial ETC defects and accompanying energy deficits are involved in the pathophysiology of progression of heart failure or represent secondary changes resulting from heart failure. Understanding the molecular basis and mechanisms for the mitochondrial ETC defects will provide a framework to devise and develop mechanism-based interventions that address the primacy of mitochondrial involvement. Specific aim 1 is to measure the rate of oxidative phosphorylation and the activity of the electron transport chain complexes in mitochondria isolated from the subsarcolemmal and the interfibrillar area of control dog heart and during heart failure during progression from early to advanced congestive heart failure, in aim 2 the site of defect in the mitochondrial complex IV in the microembolism model will be examined by determining kinetics, the amount of complex IV, the subunit composition, cytochrome content, and the lipid environment, especially cardiolipin. Specific aim 3 will be to determine the site of defect in complex III in the pacing-induced model by determining partial reactions, components, and the lipid environment. In aim 4 mitochondrial oxidative phosphorylation and electron transport chain activity will be used as an endpoint in the therapeutic trials with both models of heart failure. Aim 5 will measure oxidative phosphorylation and electron transport chain activities in skeletal muscle mitochondria isolated from dogs with microembolisation-and pacing-induced heart failure to determine whether skeletal muscle mitochondrial function is affected in both animal models. These studies would strongly suggest that a humoral factor(s) may affect skeletal muscle mitochondrial metabolism in both models.